Situational Anorgasmia Treatment Options?

Howdy folks...I'm hoping that there are other folks here who can shed some light on my current situation.

My current boyfriend suffers from a condition known as “situational anorgasmia”, and I guess it’s something that may kill our fledgling relationship. A little background info: I’m a 29-year-old female, I’ll never look like a super model, but I’m still pretty cute and adventurous in the bedroom. I have a moderate to high sex drive, and fairly good self esteem. Aside from some forgettable one-night stands, I’ve never had issues reaching orgasm with previous partners. He’s 29, and he was born with a physical deformity (missing one arm) but is otherwise physically healthy. He eats extremely well, doesn’t smoke, and he exercises on a regular basis. The problem is, he can come through oral or having sex with my breasts, but he often has a hard time maintaining an erection during vaginal intercourse, let alone reaching orgasm. His penis is larger than average, but definitely not monstrously big, and he thinks that my vagina might be “too small”. He’s admitted that he’s only been able to come through vaginal intercourse a few times with one or two previous partners.

I’m a tad skeptical of this theory as previous partners of mine have been similarly endowed, if not larger, and they’ve never complained about difficulty with full on penetration. I know that he didn’t really start dating until a few years ago, and his sex life was mainly comprised of awkward one-night stands, and masturbating to porn (the latter is something he still does on a regular basis, and I have no issue with this whatsoever). I know he’s had a lot of self-confidence issues regarding his birth defect in the past, and continues to go to therapy to cope with it. He’s an amazing person, who is super ambitious, really good looking, while still being a fun, down to earth dork (what more can a girl ask for?). According to him, this is his first real relationship, and I’m really trying to be supportive and understanding. We have a great time outside of the bedroom, and I don’t want pressure him too much about this, but at the same time, I love sex, and I’d be lying if I said that I could do without it. He’s suggested that I look into finding a FWB, but I definitely don’t enjoy having sex on a purely physical level, and he’s admitted that the idea would make him uncomfortable.

I’m inclined to believe that this issue is mainly psychological in nature, but I wonder if anything else would help (i.e. toys, stimulants, sensate focus exercises, abstaining from masturbation etc). Any suggestions? I don’t want to throw in the towel this early in the game, but at the same time, I’m going up the walls with sexual frustration.